Inflatable restraint systems or “airbag” systems have become a standard feature in many new vehicles. These systems have made significant contributions to automobile safety; however, as with the addition of any standard feature, they increase the cost, manufacturing complexity and weight of most vehicles. Technological advances addressing these concerns are therefore welcomed by the industry. In particular, the gas generator or inflator used in many occupant restraint systems tends to be the heaviest, most complex component. Thus, simplifying the design and manufacturing of airbag inflators, while retaining optimal function, has long been a goal of automotive engineers.
Typical inflators are constructed having an elongate metallic body. Because many inflators utilize pyrotechnic gas generant compounds to produce inflation gas for the associated airbag, the inflator structure is necessarily robust, making such inflators correspondingly heavy. An increasingly popular and useful inflator style uses multiple, selectively activated gas generant charges. In such systems, the multiple propellant beds disposed within the inflator body may be ignited either simultaneously or serially. Certain vehicle and occupant parameters may justify firing both propellant beds in the event of a crash. Other scenarios may be best addressed by firing only one of the propellant charges, or firing the charges sequentially, with a delay between the two events. In order to avoid sympathetic ignition of one charge during firing of the other, the combustion chambers must generally be fluidly isolated. The relatively large forces on the inflator generated by the combustion of pyrotechnics therein requires the internal partitions and other structural members of the inflator that fluidly isolate the charges to be relatively sturdy, further adding to the weight of the inflator.
Various schemes have developed for constructing sturdy, internally partitioned multi-chamber inflators. One approach involves inserting a partition into the interior of the inflator, then crimping or roll-forming the inflator body to retain the partition. This approach has proven effective; however, in many circumstances a heavier-duty/thicker inflator body must be used that will withstand the crimping and/or roll forming process. Such inflator bodies can be quite heavy, and the manufacturing process is relatively complicated given processing steps necessary to secure the internal partitions.
Yet another concern is repeatability of performance of the gas generator. Propellant springs or cushions are employed to prevent fracture of the propellant thereby maintaining a relatively constant propellant surface area of combustion. Additionally, certain propellants may be hygroscopic wherein the absorption of humidity and/or water may inhibit expected burn characteristics and therefore may result in performance variability of an associated airbag cushion during a crash event. Even though useful in preventing the fracture of propellant, propellant springs or cushions add to the manufacturing complexity and cost, and to the weight of the overall inflator.
Certain gas generating compositions or auto-ignition compositions contain constituents that contain chlorine, such as potassium perchlorate or potassium chlorate. These oxidizers may liberate chlorine-containing products over extended periods of time that are typically managed by constituents contained within each composition, such as clay or calcium oxide. The concern with utilizing clay or calcium oxide is that the relative amount of solids released after inflator activation is increased as compared to compositions that do not contain metal-containing constituents. It would be an improvement in the art to manage chlorine-containing products residing within the inflator without the use of metal-containing constituents in the respective composition, thereby increasing the relative mols of gas produced per gram of gas generant while continuing to manage the chlorine-containing products to optimize the performance of the inflator.
U.S. Pat. No. 6,779,812 to Ishida et al. describes an inflator containing silicone cushioning members made from silicon rubber and silicon foam. Ishida fails to recognize the problem of absorption of chlorine-containing products. In particular, Cole-Parmer® recognizes the general incompatibility of chlorine-containing products and silicone because of degradation of the silicone. Accordingly, in the presence of chlorine-containing products, silicon-based products are subject to chemical degradation thereby detracting from their cushioning ability in an inflator for example. See the chemical resistance charts of Cole-Parmer® on the web. Accordingly, Ishida fails to recognize the general incompatibility of silicon-containing cushions within a gas generator containing chlorine-containing products. In automotive gas generators, the shelf-life of the gas generator must meet customer specification and safety requirements. As such, vibration control relative to the propellant and management of the chlorine-containing decomposition products is desirable, while yet minimizing the metal-containing constituents in the various compositions.
WO 97/29151 to Frampton describes various pharmaceutical stoppers for capping vials of pharmaceutical products. The stoppers are made of elastomeric materials containing a desiccant. Frampton does not recognize the problem of chlorine-containing products affecting degradation of an elastomeric or silicone-based stopper.